The division cycle of yeast a cells is inhibited by the peptide pheromone, alpha-factor. After prolonged exposure to alpha- factor, a cells "adapt" to the pheromone and resume cell division. The proposed research examines the role of alpha-factor receptors in the control of these processes. Detailed understanding of this very basic process in yeast should provide information for a more general understanding of receptor action and cell division control in other organisms as well. A genetic approach will be applied to this problem. Mutants will be isolated which alter the responsiveness of a cells to alpha-factor. Defects in the processes that control receptor activity will be evaluated by performing pheromone binding and immunochemical assays. The control of cell division by polypeptide hormones has obvious medical significance.